It is highly desirable to provide a protective, heat dissipating package for electronic circuitry. Often, such circuitry can be potted, encapsulated or "molded," wherein an encapsulant is formed about the circuitry to yield a unitary, board-mountable package. One well known configuration for board-mountable package is a so-called dual in-line package ("DIP"), wherein electrical leads protrude from opposing sidewalls of the package. The leads are advantageously arranged to allow the package to be mounted to a circuit board by various conventional soldering processes. DIPs are widely used for packaging integrated circuits, most often in computer-related environments.
It has been long felt that power supplies, for instance, would greatly benefit from such encapsulation. However, in the pursuit of producing encapsulated, board-mounted power supply packages, it was discovered that the operation of potting or encapsulating the power supply circuitry with a room temperature vulcanizing ("RTV") silicone compound, or a conventional thermosetting epoxy molding compound through a conventional transfer molding process, seriously degraded the magnetic performance and efficiency of the magnetic devices within the power supply circuitry. As a result, the overall efficiency of the power supply plummeted below acceptable levels.
Within the core of the magnetic devices of the power supply are voids or cavities where the RTV silicone compound or epoxy molding compound infiltrates during the potting process. The compounds that permeate the cavities may cause damage to the core of the power supply circuitry when the encapsulant cures. More specifically, the compound expands and induces stresses on the core surrounding the cavity. The stress may induce magnetostriction on the magnetic material of the core thereby degrading the overall performance of the power supply. Moreover, the stress may cause the core to split rendering the heart of the power supply circuitry completely ineffective.
In the past, work-around "solutions" emerged to address this impasse. First, most conventional power supplies simply avoided the problem by remaining unpotted or unencapsulated. Unfortunately, the power supply circuits were unable to take advantage of the physical protection and additional heat-dissipation capacity that potting or encapsulation would have provided. Such unencapsulated power supplies were also difficult to mount on a circuit board due to a lack of suitable solder processes and handling surfaces.
Second, in the few conventional power supplies that were potted or encapsulated, the magnetic devices were required to be grossly overrated by design. After encapsulation, the magnetic performance of the devices degraded as anticipated, but, by sole virtue of their initial gross overrating, remained above an acceptable level. The process of encapsulation, therefore, caused a waste of material and space and produced additional inefficiencies in the power supplies. Further, the encapsulation process utterly failed to address the fundamental degradation problem.
Another related problem, with conventional encapsulated power supplies, a tendency for the magnetic devices of the power supplies to fail dramatically increased. After encapsulation, expansion of compounds in the cavities of the magnetic devices produce splits and cracks in the core of the power supplies leading to a very poor yield of acceptable devices.
Early attempts to solve the problems surrounding the encapsulation of the power supplies included-processes where the RTV compound or epoxy compound were excluded from the cavity of the core. These steps in the potting or molding process had limited successes and were often unreliable. Basically, mechanical devices, including foams of various shapes and sizes or nomex paper, were placed in the cavity of the core to exclude the compound from invading the cavity. Alternatively, epoxies with a low coefficient of thermal expansion ("CTE") were employed to dam or block the RTV compound or molding epoxy compounds from getting into the cavity.
While the aforementioned measures achieved minimal levels of success, degradation of performance due to effects of magnetostriction and splitting of the cores caused by the hydraulic forces induced by the expansion of the RTV or molding compounds in the cavities remain unacceptable. Furthermore, the mechanical devices were unable to completely match the void permitting the RTV or molding compound to fill the cavities.
Accordingly, what is first needed in the art is an understanding of the underlying effect that occurs when electronic devices are subject to forces, causing the performance of the devices to degrade and the production yield to be unacceptable. Further, what is needed (once the effects are understood) is an package for an electronic device and an associated highly economical and feasible method of manufacture for such packages that preserve the integrity and electrical performance by directly addressing the effect.